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    ABSTRACT: Morphotectonic analysis of landscape using remote sensing and GIS is an effective way of deducing the pattern and spatial variation of neotectonic activity along poorly investigated active faults. In this paper, we evaluate the neotectonic activity along a part of the seismically active but poorly understood Narmada–Son Fault (NSF), a more than 1000 km long ENE–WSW trending fault transecting through the central part of the Indian plate. The NSF in the study area is geomorphologically expressed as an ENE–WSW trending line of north facing scarps that delimit the rugged mountainous topography of the uplands to the south and the alluvial basin to the north which prominently slope away from the scarps. The scarps are developed in the south dipping basaltic flows belonging to the Deccan Trap Formation of the late Cretaceous–Eocene and continue westward into Tertiary rocks and further as a paleobank of the Narmada River. Field studies have revealed that the NSF in the study area is divisible into four morphotectonic segments (I to IV), which is attributed to the Tilakwada, Karjan, Madhumati and Rajpardi Faults cutting across the NSF. We characterize the neotectonic activity of the segments through DEM analysis, using geomorphic indices which include the mountain front sinuosity, hypsometric curves, hypsometric integral, asymmetry factor, stream length–gradient index and channel sinuosity. Interpretations of morphometric data are well supported by field data. Both the entire length of the NSF and the cross faults are found to be neotectonically active. We demonstrate that segment II has undergone the highest intensity of neotectonic activity followed by segments III, I and IV. This is corroborated by the highest elevation of scarps and the alluvial deposits, the deepest incision (~ 40 m depth) and steep northward slope of the alluvial plain in segment II. We infer that the NSF is characterized by differential uplift in recent past which agrees with the high angle reverse faulting with oblique-slip movements along the cross faults.
    Geomorphology 01/2013; s 180–181:292–306.
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    ABSTRACT: The rivers of western India are monsoon dominated and have been so throughout the late Quaternary. Sediment accumulation in these river basins has been controlled by climatic and tectonic changes over a time span from the Late Pleistocene to the recent. The lithofacies assemblages associated with the various sediment archives in the Narmada basin range from the boulders of the alluvial fans to overbank fines on the alluvial plains. Estimates, based on clast size, of stream power and competence, bed shear stress and discharge reveal that hydrological conditions during the Late Pleistocene (∼90ka) were comparable to the present day. The size of the transported clasts and the thickness of the accumulated sediment indicate the influence of basin subsidence rather than an increase in discharge. Discharge estimates based on sedimentary structures preserved in the alluvial-plain facies suggest that the channel had a persistent flow, with a low width–depth ratio and large meander wavelength. The hydrological changes during the Holocene are more pronounced where the early Holocene is marked by a high-intensity hydrological regime that induced erosion and incision of the earlier sediments. The mid-Holocene stream channel was less sinuous and had a higher width–depth ratio and a higher meander amplitude in comparison with the present-day channel. Palaeo-fluvial reconstructions based on the sediment archives in the alluvial reach of the river basin are important tools in understanding the long-term hydrological changes and the intricate fluvial architecture preserved in the Narmada River basin ensures scope for detailed studies to identify phases of weak and enhanced hydrological regimes.
    Proceedings of The Geologists Association - PROC GEOL ASSOC. 01/2010; 121(2):195-202.
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    ABSTRACT: Flooding of rivers in India is linked with the peak monsoons. Investigating the linkage between monsoonal patterns and flood history of various rivers is therefore of fundamental importance in the Indian context. In the present study, the slackwater deposits in the alluvial reaches of the Mahi river basin, western India have been documented. These occur in the ravines incised during the early Holocene on an alluvial surface comprising sediments of Late Pleistocene age. The slackwater deposits occur at elevations up to 20 m from the present river level and extend to about 500 m inland. The carbonate rich sediments forming the ravine cliffs have provided bank stability and the dissections in the ravines have helped in the accumulation of slackwater deposits due to backflooding of the floodwater from the main channel. Recent gullies have incised the sediments and exposed deposits related to major flood events. The best exposures of slackwater deposits have been observed at Dodka. The sediment succession of the slackwater deposits is dominated by bedsets and laminasets of silt and sand separated by colluvial sediments. Four events of flood deposition occurred during the mid to late Holocene. Two units of slackwater deposits, SWD 2 and 4 have been dated by IRSL at 4.6 ± 1 ka and 1.7 ± 0.5 ka. The stratigraphy of these deposits indicates that the first two slackwater units (SWD1 and SWD2) have resulted due to flooding in a regime of intense monsoon. The other two units, however, represent extreme high magnitude floods in a period of low average precipitation.
    CATENA. 01/2007; 70(3):330-339.
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    ABSTRACT: This study presents field and ground penetrating radar (GPR) data for understanding geomorphic evolution of the Kim-drainage basin in response to tectonic inversion of the Narmada–Ankleshwar block of the Cambay rift basin located on the western-continental margin of India. The Narmada–Ankleshwar block underwent continuous sedimentation up to Mio–Pliocene and subsequently was subjected to compressional inversion. Four geomorphic surfaces are recognised that formed in response to the varying degrees of tectonic activity related to phases of inversion. These are the early Pleistocene erosional surface (EPES), late Pleistocene depositional surface (LPDS), early Holocene erosional surface (EHES) and the late Holocene depositional surface (LHDS). The phases of increased tectonic activity relate to two erosional episodes, while two depositional periods relate to waning tectonic activity or quiescent periods. We show that the Narmada–Ankleshwar block suffered inversion earlier than other parts of the Cambay basin to the north of the NSF. Localisation of early inversion movements occurred in an area characterised by thinner crust and involved the development of new reverse faults and transformation of the NSF from a normal to a reverse fault. GPR studies indicate the reverse nature of the various faults in the Kim drainage basin and provide evidence of their late reactivation under compression. The study demonstrates that the parts of a large sedimentary basin can undergo inversion at different times depending on the orientation of pre-existing crustal discontinuities with respect to the controlling stress trajectories.
    Journal of Asian Earth Sciences 01/2007;
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    ABSTRACT: Late Pleistocene fluvial sediments that were deposited in a slowly sinking basin are now exposed as 30–50 m high incised vertical cliffs all along the Lower Narmada Valley in western India. The exposed fluvial deposits have been classified into two sediment packages, alluvial fan sediments overlain by alluvial plain sediments. The alluvial plain sequence has not been studied previously. It consists mainly of sands and silts and is dominated by overbank deposits. Occurrence of large scale bedforms in the alluvial plain sequence points to the existence of a large sand bed river in an alluvial plain setting. The major sedimentary facies in stratigraphic order include large channel fills, giant epsilon cross bedded strata, overbank fines occurring in horizontal, massive and undulatory stratified forms associated with crevasse splay and backswamp deposits, and a reddish brown palaeosol overlain by thinly stratified sands and silts at the top of the exposed sediment succession. Large sized channel fills occur at two stratigraphic levels, which are morphologically similar and are indicative of high rates of deposition and avulsion. The large channel fill structures and the giant epsilon cross bedded strata indicate a large single channel river that was consistently 10–15 m deep and about 70–80 m wide even during the dry seasons. These dimensions are larger than those of the present day Narmada River at low discharge levels. The overbank sediments indicate rapid deposition through frequent overbank floods and floodplain aggradation by a laterally shifting river. Available chronologic data suggests that the reddish brown palaeosol correlates with a regional phase of pedogenesis in the alluvial plain of Gujarat prior to the Last Glacial Maximum (LGM). The thinly stratified sands and silts overlying the palaeosol were deposited by a considerably depleted but perennial river during the arid phase of the Last Glacial Maximum. Overall, the alluvial plain sediments of the Lower Narmada valley, particularly those below the palaeosol, have been attributed to a hyper-avulsive large river with low sinuosity whose high discharge levels were determined primarily by a large catchment area further to the east and not by the semiarid climate prevailing in the Gujarat alluvial plain during the upper part of the Late Pleistocene. The study concludes that the Narmada River has maintained a large catchment at least since the last 100ka, however, the river was characterised by a much bigger channel during much of the Late Pleistocene with discharge levels higher than the present day.
    Journal of Asian Earth Sciences 01/2005; 24(4):433-444.
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    ABSTRACT: A study of a well-exposed late Quaternary calcrete-conglomerate sheet from Gujarat, western India provides some insights on bedform migration and bar evolution in sub-humid monsoon-influenced rivers. The architecture of the conglomerate sheet is defined by the presence of two elements, channel (CH) and gravel-bar (GB). This architectural simplicity is remarkable and may be typical of monsoon-influenced rivers that show dominance of 3D dunes. In the initial stage (1), the river was sand-load dominated as seen in the presence of cross-bedded sands at the base. Associated with this stage was a channel element (CH1) at the northern extremity of the outcrop. During stage (2), bank-excavated blocks were redistributed in the channel, which aided the appearance of gravel mesoforms within depressions on the channel bed and subsequent low stage sedimentation leading to the formation of channel element CH2. In stage (3), gravel dunes covered the entire channel bed and are separated from the preceding deposits by a channel lag. Falling stage dissection of the bar was accompanied by relocation of the flow, along a smaller channel (represented by channel element CH3) at the northern end of the outcrop and bar top dissection. This history of bar evolution compares well with the central-bar initiation and transverse bar braiding mechanisms described in flume studies except for change in bed-material. Palaeocurrents during the termination of stage-3 showed typical patterns of convergence and divergence of bedforms in the southern extremity of the outcrop whereas the palaeocurrent directions are more consistent in the central regions. This could be related to dune combination and splitting.
    Sedimentary Geology 01/2003; 157:277-289.
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    Geomorphology 01/2003; 50(4):367-367.
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    ABSTRACT: The fluvial systems and landscape of the drylands of western India have preserved evidence of Late Quaternary environmental and tectonic changes. Data on the fluvial systems of Mainland Gujarat, Saurashtra and Kachchh have been synthesised to evaluate the roles of geological factors in the evolution of these drylands.Mainland Gujarat is largely underlain by the flat alluvial plain, and has a structurally controlled fluvial system that originates in the eastern uplands. The fluvial system of Mainland Gujarat shows deeply incised valleys, entrenched meanders, extensively developed ravines and uplifted terraces, which have preserved a Late Quaternary succession of continental (fluvial and aeolian) and marine sediments dating back to . Marine sediments correspond to the transgressive phases of the last interglacial and post-glacial maximum . The overlying alluvial sediments suggest deposition by ephemeral rivers in varied fluvial depositional environments under a semi-arid to sub-humid climatic regime with periods of intense pedogenesis. The sedimentation can be correlated with marine isotopic stages (MIS) 5 and 3. The fluvial sediments are buried under a thick blanket of aeolian sediments, which are indicative of enhanced dune building activity in the Thar Desert and are correlatable to the global arid phase of the last glacial maximum. The post-aeolian tectonic uplift triggered severe erosion of Late Pleistocene sediments and 40– deep incised fluvial valleys were formed. This erosional phase suggests a resumption of fluvial activity, which coincided with the rapidly rising sea level on the west coast during the Early Holocene. The Holocene marine and fluvial aggradation was initiated within the incised fluvial valleys around and continued uninterrupted until . These sediments now occur as raised valley fill terraces suggesting a Late Holocene uplift further corroborated by low to moderate seismic activity during historical times.The landscape of Saurashtra is marked by flat-topped basaltic (trappean) ridges and a highly varied coastline where a narrow belt of low ridges and cliffs of miliolite limestones and other shore deposits are found. The fluvial system of Saurashtra shows a radial drainage pattern. The channels have steep banks in the hilly regions and show significant deflections before meeting the sea. Evidence of last interglacial high sea levels are found on the coastal cliffs of southern Saurashtra in the form of oyster reefs and notches of various types which now occur at higher levels. A net sea level rise of consistent with the global sea level estimates at has been obtained by recent studies after decoupling the tectonic component. Dating of Late Pleistocene and Holocene sea levels on this coast suggest continued uplift of Saurashtra since even though the sea level continued to fluctuate. The Holocene high sea submerged a considerable stretch of land including the Okha Rann on the northern Saurashtra coast and isolated patches in and around the river mouths on the southern coast. The short, straight and parallel courses of rivers in the direction of tectonic slope, incised and confined channel belts also suggest a strong component of tectonic uplift. The continental sediments exposed in these river valleys have however remained uninvestigated leading to lack of palaeoclimatic data.A remarkable control of structure on landscape evolution is depicted by the Kachchh peninsula. The fluvial system exhibits the characteristics of drainage flowing along tectonically provided slopes. The overall drainage pattern of Kachchh shows excellent correlation with N–S trending transverse fault patterns. The transverse fault system has brought out changes in the landscape of Kachchh though the Kachchh rift basin evolved along E–W latitudinal faults. The Quaternary deposits occur in the form of miliolite limestones, colluvial and alluvial fans, fluvial sands and silts, and Rann sediments. Significant sedimentologic details on these sediments are lacking. However, the marine incursions seem to correlate with the adjacent Saurashtra and Mainland Gujarat.
    Quaternary International 01/2003;
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    ABSTRACT: Geomorphic data combined with stratigraphic studies provide significant information to constrain timing and amount of fault movement. The lower Narmada valley lies astride the Narmada–Son Fault (NSF), an important ENE–WSW-trending tectonic element responsible for the current intraplate seismicity being experienced in the central part of the Indian plate. Varying nature and degree of tectonic movements along the NSF during Late Pleistocene and Holocene have produced four geomorphic surfaces in the lower Narmada valley: the alluvial plain (S1), ravine surface (S2), a gravelly fan surface (S3) and the valley fill terrace surface (S4). Two major phases of tectonic movements in a compressive stress regime are recorded along the NSF: slow synsedimentary subsidence of the basin during Late Pleistocene due to differential movement, followed by inversion of the basin during the Holocene marked by differential uplift along the NSF. The study suggests that the inversion of the basin is in response to the significant increase in the intensity of compressive stresses in the Indian plate mainly during the Early Holocene. The present incisive drainage and recent seismic activity indicate that the compressive stresses continue to accumulate along the NSF due to continued northward movement of the Indian plate.
    Geomorphology. 01/2002;
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    ABSTRACT: Late Quaternary deposits in Mainland Gujarat contain sediments deposited in subhumid and semi-arid climates. The 30–35 m succession shows the presence of Vertisols at the base and a red-bed horizon (ferric Calcisol when pedogenic in origin) that roughly bisects the succession. A widespread development of calcretes is observed throughout the succession. The various varieties of calcrete include pedogenic calcrete, groundwater calcrete, calcrete conglomerate (transported calcrete) and rhizogenic calcrete. Pedogenic calcrete nodules associated with Vertisols and the red-soil show marked differences in morphology, dimensions and the distribution of microscopic features. These differences arise due to contrasting climate-controlled physicochemical environs under which they formed. Pedogenic calcrete nodules associated with Vertisols acquire large (5–10 cm) dimensions and are characterised by either showing the presence of a nucleus of soil-matter or showing a dense micritic groundmass cut by thick sparitic veins. In contrast, calcrete nodules that formed in the red-soil are <3 cm in size and do not exhibit dense networks of sparitic veins. Calcretes associated with Vertisols and the ferric Calcisol also exhibit differences in the morphology of rhizoliths. These differences also show up in the distribution of microfabrics of calcretes. Grain coats are present in rhizogenic and pedogenic calcretes, but absent in groundwater calcretes and less profuse in hydromorphic soil calcretes. Clotted micrite is present in all types except groundwater calcretes. Sparitic veins, however, are observed in each type, but are relatively less developed in groundwater calcretes. A similar distribution of displacive and replacive textures is also seen, although some grains in groundwater calcretes showed signs of corrosion. The Vertisol-associated calcretes represent a subhumid (500–700 mm) climate, whereas the red-soil calcretes suggest a semi-arid (100–500 mm) climate. Calcretes from the Vertisol association show a range in δ13C composition constrained between −9‰ and −5‰, whereas the red-soil calcretes exhibit the whole spectrum of values from −9‰ to −1‰. Based on mineralogical associations, calcretes, usually taken to reflect semi-arid episodes in the Earth's history, may be classified further. Calcretes, when associated with sepiolite/palygorskite, suggest an arid climate (mean annual rainfall=50–100 mm), when associated with smectite, haematite and the absence of hydromorphism, a semi-arid climate (mean annual rainfall=100–500 mm), and when found in smectitic Vertisols, subhumid climates (mean annual rainfall=500–700 mm).
    Palaeogeography Palaeoclimatology Palaeoecology 01/2000;
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